A variety of devices and methods are used to clean slag and similar deposits from boilers, furnaces, and similar heat exchange devices. Some of these rely on chemicals or fluids that interact with and erode deposits. Water cannons, steam cleaners, pressurized air, and similar approaches are also used. Some approaches also make use of temperature variations. And, of course, various types of explosive, creating strong shock waves to blast slag deposits off of the boiler, are also very commonly used for deslagging.
The use of explosive devices for deslagging is a particularly effective method, as the large shock wave from an explosion, appropriately positioned and timed, can easily and quickly separate large quantities of slag from the boiler surfaces. But the process is costly, since the boiler must be shut down (i.e. brought off line) in order to perform this type of cleaning, and valuable production time is thereby lost. This lost time is not only the time during which the cleaning process is being performed. Also lost are several hours prior to cleaning when the boiler must be taken off line to cool down, and several hours subsequent to cleaning for the boiler to be restarted and brought into full operational capacity.
Were the boiler to remain on-line during cleaning, the immense heat of the boiler would prematurely detonate any explosive placed into the boiler, before the explosive has been properly positioned for detonation, rendering the process ineffective and possibly damaging the boiler. Worse, loss of control over the precise timing of detonation would create a serious danger for personnel located near the boiler at the time of detonation. So, to date, it has been necessary to shut down any heat exchange device for which explosives-based deslagging is desired.
Several U.S. patents have been issued on various uses of explosives for deslagging. U.S. Pat. Nos. 5,307,743 and 5,196,648 disclose, respectively, an apparatus and method for deslagging wherein the explosive is placed into a series of hollow, flexible tubes, and detonated in a timed sequence. The geometric configuration of the explosive placement, and the timing, are chosen to optimize the deslagging process.
U.S. Pat. No. 5,211,135 discloses a plurality of loop clusters of detonating cord placed about boiler tubing panels. These are again geometrically positioned, and detonated with certain timed delays, to optimize effectiveness.
U.S. Pat. No. 5,056,587 similarly discloses placement of explosive cord about the tubing panels at preselected, appropriately spaced locations, and detonation at preselected intervals, once again, to optimize the vibratory pattern of the tubing for slag separation.
Each of these patents discloses certain geometric configurations for placement of the explosive, as well as timed, sequential detonation, so as to enhance the deslagging process. But in all of these disclosures, the essential problem remains. If the boiler were to remain on-line during deslagging, the heat of the boiler would cause the explosive to prematurely detonate before it is properly placed, and this uncontrolled explosion will not be effective, may damage the boiler, and could cause serious injury to personnel.
U.S. Pat. No. 2,840,365 appears to disclose a method for introducing a tube into "a hot space such as an oven or a slag pocket for an oven" prior to the formation of deposits in the hot space; continuously feeding a coolant through the tube during the formation of deposits in the hot space, and, when it is time to break the deposits, inserting an explosive into the tube after the formation of the deposits while the tube is still somewhat cooled, and detonating the explosive before it has a chance to heat up and undesirably self-detonate. (See, e.g., col. 1, lines 44-51, and claim 1) There are a number of problems with the invention disclosed by this patent.
First, the hot space according to this patent must be thoroughly prepared and preconfigured, in advance, for the application of this method, and the tubes that contain the coolant and later the explosive, as well as the coolant feeding and discharge system, must be in place on a more or less permanent basis. The tubes are "inserted before the deposits begin to form or before they are formed sufficiently to cover the points where one wishes to insert the tubes" and are "cooled by the passage of a cooling fluid . . . therethrough during operation." (col. 2, lines 26-29 and col. 1, lines 44-51) It is necessary "to provide sealable holes in several bricks for allowing the tube . . . to be inserted, or . . . to remove the bricks during operation of the furnace so that a hole is formed through which the tube may be inserted." (col. 2, lines 32-36) The tubes are supported "at the back end of the pocket upon supports made for the purpose, e.g., by a stepped shape of the back of the wall . . . [or] at the front end or in front of and in the wall . . . [or by having] at least the higher tubes . . . rest immediately upon the deposits already formed." (col. 2, lines 49-55) A complicated series of hoses and ducts are attached for "feeding cooling water . . . and discharging said cooling water." (col. 3, lines 1-10, and FIG. 2 generally) And, the tubes must be cooled whenever the hot space is in operation to prevent the tubes from burning and the water from boiling. (see, e.g., col. 3 lines 14-16 and col. 1, lines 44-51) In sum, this invention cannot simply be brought onto the site of a hot space after deposits have formed and then used at will to detonate the deposits while the hot space is still hot. Rather, the tubes must be in place and continuously cooled essentially throughout the entire operation of the hot space and the accumulation of deposits. And, significant accommodations and preparation such as tube openings and supports, the tubes themselves, and coolant supply and drainage infrastructure, must be permanently established for the associated hot space.
Second, the method disclosed by this patent is dangerous, and must be performed quickly to avoid danger. When the time arrives to break the slag deposits, "the pipes . . . are drained," various cocks, hoses, bolts and an inner pipe are loosened and removed, and "explosive charges are now inserted [into the pipe] . . . immediately after termination of the cooling so that no danger of self-detonation exists, because the explosive charges cannot become too hot before being exploded intentionally." (col. 3, lines 17-28) Then, the "tubes are exploded immediately after stopping the cooling at the end of the operation of the furnace . . . " (col. 1, lines 49-51) Not only is the process of draining the pipe and readying it to receive the explosive fairly cumbersome, it must also be done in a hurry to avoid the danger of premature explosion. As soon as the coolant flow is ceased, time is of the essence, since the tubes will begin to heat up, and the explosives must be placed into the tubes and purposefully detonated quickly, before the heating of the tube become so great that the explosive accidentally self-detonates. There is nothing in this patent that discloses or suggests how to ensure that the explosive will not self-detonate, so that the process does not have to be unnecessarily hurried to avoid premature detonation.
Third, the pre-placement of the tubes as discussed above constrains the placement of the explosive when the time for detonation arrives. The explosives must be placed into the tubes in their preexisting location. There is no way to simply approach the hot space after the slag accumulation, freely choose any desired location within the hot space for detonation, move an explosive to that location in an unhurried manner, and then freely and safely detonate the explosive at will.
Fourth, it may be inferred from the description that there is at least some period of time during which the hot space must be taken out of operation. Certainly, operation must cease long enough for the site to be prepared and fitted to properly utilize the invention as described earlier. Since one object of the invention is to "prevent the oven . . . to be taken out of operation for too long a time," (col. 1, lines 39-41, emphasis added), and, since the "tubes are exploded immediately after stopping the cooling at the end of the operation of the furnace or the like" (col. 1, lines 49-51, emphasis added), it appears from this description that the hot space is in fact shut down for at least some time prior to detonation, and that the crux of the invention is to hasten the cooling of the slag body after shutdown so that detonation can proceed more quickly without waiting for the slag body to cool down naturally (see col. 1, lines 33-36), rather than to allow detonation to occur while the hot space is in full operation without any shutdown at all.
Finally, because of all the site preparation that is needed prior to using this invention, and due to the configuration shown and described for placing the tubes, this invention does not appear to be usable across the board with any form of hot space device, but only with a limited type of hot space device that can be readily preconfigured to support the disclosed horizontal tubing structure as disclosed.
Luxemburg patent no. 41,977 has similar problems to U.S. Pat. No. 2,840,365, particularly: insofar as this patent also requires a significant amount of site preparation and preconfiguration before the invention disclosed thereby can be used; insofar as one cannot simply approach the hot space after the slag accumulation, freely choose any desired location within the hot space for detonation, move an explosive to that location in an unhurried manner, and then freely and safely detonate the explosive at will; and insofar as the types of hot space devices to which this patent applies also appear to be limited.
According to the invention disclosed by this patent, a "blasting hole" must be created within the subject hot space before the invention can be used. (translation of page 2, second full paragraph) Such holes are "drilled at the time of need or made prior to the formation of the solid mass." (translation of paragraph beginning on page 1 and ending on page 2) Since the device for implementing the process of the invention "includes at least a tube that permits feeding the cooling fluid into the bottom of the blasting hole" (translation of page 2, fourth full paragraph) and, in one form of implementation, "a retaining plate . . . positioned at the bottom of the blast hole (translation of paragraph beginning on page 2 and ending on page 3), and since it is a key feature of the invention that the blast hole is filled with coolant prior to and during the insertion of the explosive, it may be inferred from this description that the blast hole is substantially vertical in it orientation, or at least has a significant enough vertical component to enable water to effectively accumulate and pool within the blast hole.
Because the subject hot space must be preconfigured with a blast hole or holes (with implicitly at least a substantial vertical component) before this invention can be used, it is again not possible to simply approach an unprepared hot space at will after deposits have accumulated, and detonate at will. Since the coolant and the explosive must be contained within the blast holes, it is not possible to freely move and position the explosive wherever desired within the hot space. The explosives can only be positioned and detonated within the blast holes pre-drilled for that purpose. Due to the at least partially vertical orientation of the blast holes, the angle of approach for introducing the coolant and the explosive is necessarily constrained. Also, while it is not clear from the disclosure how the blast holes are initially drilled, it appears that at least some amount of boiler shutdown and/or disruption would be required to introduce these blast holes.
Finally, in both of these cited patents, the components which hold the coolant (the tubes for U.S. Pat. No. 2,840,365 and the blast holes for LU 41,977) reside within the hot space, and are already very hot when the time arrives to deslag. The object of both of these patents, is to cool these components down before the explosive is introduced. U.S. Pat. No. 2,840,365 achieves this by virtue of the fact that the tubes are continuously cooled throughout the operation of the hot space, which, again, is very disruptive and requires significant preparation of and modification to the hot space. And LU 41,977 clearly states that "[a]ccording to all its forms of implementation, the device is put in place without a charge for the purpose of cooling the blast hole for a few hours with the injection fluid (translation of page 4, last full paragraph, emphasis added). It would be desirable to avoid this cooldown period altogether and therefore save time in the deslagging process, and to simply introduce a cooled explosive into a hot space at will without any need to alter or preconfigure the boiler, and to then detonate the cooled explosive at will once it has been properly placed in whatever detonation location is desired. And most certainly, the application of LU 41,977 is limited only to hot spaces into which it is feasible to introduce a blast hole, which appears to eliminate many types of heat-exchange device into which it is not feasible to introduce a blast hole.